Bioleaching of sulphide containing ores is a phenomena which has been utilized for a number of years. In particular, bacterially assisted leaching of ores containing chalcopyrite, usually in combination with pyrite, has been extensively caried out in the presence of acidophilic Thiobacillus ferrooxidans, to recover copper from the chalcopyrite. It is known however, that other bacteria either alone or in combination with T. ferrooxidans, can accomplish the same purpose. Previously, the leaching solution for such ores was an aqueous acidic one containing a suitable bacterial nutrient. The low pH was favoured by the usually acidophilic bacteria, and also ensured solubilization of iron and other metals. Methods have been proposed in the past to increase the rate of reaction of the foregoing basic process. Such methods include addition of an appropriate amount of surfactant as disclosed in U.S. Pat. No. 3,266,889 to Duncan et al, and addition to the leaching medium of a catalytic amount of silver as is shown in U.S. Pat. No. 3,856,913 to McElroy et al. Carbon dioxide enriched air is typically provided during the leaching. Although the reactions which occur are not fully understood, the overall reactions in either the basic process described or the processes in the McElroy and Duncan patents appears to be: EQU 12CuFeS.sub.2 +51O.sub.2 +22H.sub.2 O.fwdarw.12CuSO.sub.4 +4H.sub.3 OFe.sub.3 (SO.sub.4).sub.2 (OH).sub.6 +4H.sub.2 SO.sub.4 ( 1) EQU 12FeS.sub.2 +45O.sub.2 +34H.sub.2 O.fwdarw.4H.sub.3 OFe.sub.3 (SO.sub.4).sub.2 (OH).sub.6 +16H.sub.2 SO.sub.4 ( 2)
The solubilized copper, and the silver (as used in the process of the McElroy patent) are recovered by well known means.
A potential disadvantage of the foregoing prior processes is that they produce sulphuric acid. Because the disposal of sulphuric acid could constitute an environmental hazard, a neutralization step is required following leaching. Various hydrometallurgical processes for recovering copper from ores such as chalcopyrite and bornite and producing sulphur in the elemental form are known though. For example, U.S. Pat. No. 3,637,371 to Mackiw et al discloses a high temperature, oxygen pressure acid leach process for converting chalcopyrite to copper sulphate, basic ferric hydroxide and elemental sulphur. U.S. Pat. No. 3,949,051 to Pawlek discloses a process using silver to enhance copper leach rates and extraction from very finely ground chalcopyrite at high temperature and pressure. U.S. Pat. No. 3,886,257 to Snell again discloses a process for oxidatively leaching copper from copper ores in the presence of a catalytic amount of silver ions and an oxidative agent such as ferric sulphate, dilute sulphuric acid in the presence of added oxygen, or concentrated sulphuric acid.
It would be desirable then to have a relatively rapid bacterially assisted process for producing a metal from the metal sulphide containing ore, such as copper from chalcopyrite containing ore, which process does not result in the production of sulphuric acid, but preferably results in sulphide being oxidized to elemental sulphur, and which process can be carried on at relatively low temperature and relatively low pressure. Such a process would avoid a neutralization step following leaching, and would also result in readily separable and economically valuable, sulphur.